The present invention relates to a lens unit used for a camera, and in particular, to the lens unit which is retractable to become compact while carried, and to a camera having the same lens unit.
In the past, a great number of compact cameras which users can more easily carry, are well known, wherein the lens unit protrudes for photographing, and retracts to a compact size for not photographing.
However, even though the lens unit is retracted along the optical axis to minimize the clearance between each lens, it is impossible to retract the lens unit to less than the summation of the thickness of all lenses and the retracted clearance between adjacent lenses. In order to overcome this problem, proposed is a specific lens and an image pickup device which are moved out of the optical axis, and other lens groups are retracted along the optical axis so that the thickness of the lens unit is reduced when the lens unit is retracted.
As such cameras, disclosed is one in which the image pick up device is moved out of the optical path, and the lens groups are retracted along the optical axis, or another camera is disclosed which incorporates a lens unit whose backmost lens group and image pickup device are integrally moved from the optical path. (Patent Documents 1 and 2)
Further, disclosed is a camera wherein among three lens groups within the lens units, the third lens group as the backmost is used for focusing and is pivoted 180 degrees about a supporting shaft for the movement, while the first and the second lens groups are retracted along the optical axis (Patent Document 3).    [Patent Document 1] Unexamined Japanese Patent Publication 11-258676    [Patent Document 2] Unexamined Japanese Patent Publication 11-109203    [Patent Document 3] Unexamined Japanese Patent Publication 2003-149723
Concerning cameras using an image pickup device, the size of the surface of the image pickup device is about ⅓-½ inches, which is less than the film frame of a camera using silver film. Accordingly, though the maximum aperture F of an image capturing lens of the camera using the image pickup device is already very small, the camera can be downsized still further. However, due to this, the tolerable error margins of the image capturing lens becomes dramatically less than the conventional silver halide cameras.
The cameras disclosed in Patent Documents 1 and 2 feature a method in which the image pickup device is moved for focusing, and it is very difficult to correctly determine the stopping position of the image pickup device along the optical axis with high repeatability. When the optical axial position of the image pickup device fluctuates, the focusing lenses cannot be reliably controlled, which is of course unacceptable.
In order to move the lens groups outside the optical axis, the camera disclosed in Patent Document 3 features a method in which a specific gear is mounted on an arm section of the lens frame, another gear engaging the specific gear is driven so that the lens group rotates about a shaft passing through the arm section, and thereby, the lens group is moved. According to this structure, a specific actuator is employed so that the lens group, which is to be moved outside the optical axis, can be driven for focusing along the optical axis. To employ two actuators, the mechanical space must be enlarged whereby the production cost increases, and additionally, there remains the major problem of determining the optical axial position of the lens group being moved.